While the ability to deposit epitaxial coatings on textured substrates has been demonstrated in the past, the methods to produce these coatings have several disadvantages such as being relatively slow as well as requiring expensive vacuum and other extensive equipment. Furthermore, the use of epitaxial coatings has been limited to only a few applications in the past. With the advent of combustion chemical vapor deposition (CCVD), a new, quicker and less expensive method of producing these coatings has been realized. In addition to the cost savings and reduced environmental impact achieved by using the CCVD method, the use of epitaxial coatings has been expanded to several other fields.
The chemical vapor deposition processes that have been so successful include the combustion chemical vapor deposition (CCVD) processes described in U.S. Pat. Nos. 5,652,021; 5,858,465; and 5,863,604, and issued to Hunt et al. These patents, which are hereby incorporated by reference, disclose methods and apparatus for CCVD of films and coatings wherein a reagent and a carrier medium are mixed together to form a reagent mixture. The mixture is then ignited to create a flame or the mixture is fed to a plasma torch The energy of the flame or torch vaporizes the reagent mixture and heats the substrate as well. These CCVD techniques have enabled a broad range of new applications and provided new types of coatings, with novel compositions and improved properties. In addition to these three patents, U.S. Pat. No. 5,997,956, also issued to Hunt et al. describes a further method of CVD involving the use of a thermal spray with near supercritical and supercritical fluid solutions. The coating processes disclosed in this patent are also useful for forming the epitaxial coatings of the present invention, and this patent is incorporated by reference as well.
U.S. Pat. Nos. 5,739,086, issued on Apr. 14, 1998 and 5,741,377 issued on Apr. 21, 1998, both to Goyal et al teach textured articles having a rolled and annealed, biaxially textured metal substrate and an epitaxial coating deposited thereon. The articles are manufactured by rolling and annealing a metal base preform to create a biaxially textured substrate with a face-centered cubic, body-centered cubic or hexagonal closed-packed crystalline structure. Onto the surface of the substrate, an epitaxial layer is deposited to form a biaxially textured laminate. A buffer layer in the form of an epitaxial barrier layer may first be deposited, followed by an epitaxial superconducting layer deposited thereon. A pulsed laser technique, as well as several other techniques may be used to deposit the superconducting and buffer layers.
U.S. Pat. No. 5,523,587 issued on Jun. 4, 1996 to Kwo is drawn toward a method for low temperature growth of epitaxial silicon, and devices produced using this method. The thin layer of epitaxial silicon is grown at temperatures at or below 300° C. by first providing a substrate, forming a dielectric buffer layer and then growing the epitaxial silicon on the buffer layer. A directed ion beam bombards the buffer layer while it is being deposited to provide the desired orientation. The low temperatures used in this deposition process allow for the use of light-weight substances such as glass coated plastics to reduce the weight of displays in hand held and lap-top electronic equipment. These deposition methods, however, require vacuum and other limiting deposition parameters.
U.S. Pat. No. 5,968,877, issued on Oct. 19, 1999 to Budai et al. discloses high Tc YBCO superconductor deposited on a biaxially textured Ni substrate. One or more epitaxial buffer layers are deposited on the Ni substrate prior to the deposition of the c-axis oriented YBCO top layer. The epitaxial buffer layers include CeO2, yttria-stabilized ZrO2 and palladium, while the superconducting layer is YBa2Cu3O7−6. The buffer layers are deposited by pulsed-laser, electron beam evaporation, or sputtering methods.
International Patent Application, Publication No. WO 99/15333, published on Apr. 1, 1999 to Fritzemeier et al. is drawn to superconducting articles with epitaxial layers. The articles are produced in a partial vacuum environment using a gas phase method. The epitaxial or buffer layers may include CeO2, yttria-stabilized ZrO2, LaAlO3, SrTiO3, LaNiO3, LaCuO3, SrRuO3, CaRuO3, NdGaO3 and NdAlO3. By using the gas phase method, the epitaxial buffer layers are formed with a surface having a pore density of less than about 500 pores per mm2.
U.S. Pat. No. 5,741,406, issued on Apr. 21, 1998 to Barnett et al. discloses solid oxide fuel cells having dense yttria-stabilized zirconia (YSZ) electrolyte films and a method of depositing these electrolyte films. The YSZ electrolyte thin films are deposited on a lanthanum strontium manganite (LSM) substrate using an ion-assisted deposition technique such as sputtering. By applying a DC bias voltage to the LSM substrate, ion bombardment of the YSZ film is provided during deposition. The ion bombardment leads to removal of material from protrusions, re-deposition into pores and a more planar film surface.
None of the above references and patents, taken either singly or in combination, is seen to provide an epitaxial thin film, suitable for use as a buffer layer in applications requiring, inter alai, low-loss dielectric substrates with high permittivity.